It is well recognized that, among naturally occurring and synthetic molecular sieves, aluminum silicate molecular sieves have the most important and most effective crystal composition. X-ray diffraction testing shows that most of the aluminum silicate crystals have clear and different crystal structures and ordered open-framework structures. Different types of molecular sieves have different characteristic open-framework crystal structures.
The different types of molecular sieve are defined by International Zeolite Association (IZA) as different structure codes, such as FAU, MFI, BEA and CHA. As is well known, a molecular sieve SSZ-13 has a CHA topological structure and its synthesis method was firstly disclosed in U.S. Pat. No. 4,544,538 on Oct. 1, 1985. In U.S. Pat. No. 4,544,538, under a condition where the organic cation N,N,N-trimethyl-1-amantadine (TMAA+) is used as a structure-directing agent, the molecular sieve SSZ-13 may be synthesized. However, due to the structure-directing agent used is greatly expensive, the synthesis cost of the molecular sieve SSZ-13 is rather high, thereby limiting the application of the molecular sieve SSZ-13 in commercial production. The present invention has provided a method for synthesizing the molecular sieve SSZ-13 without using the expensive TMAA+ as a structure-directing agent.
It is disclosed in the description of U.S. Pat. No. 60/826,882 applied by Zones on Sep. 25, 2006 that Zones developed a method for synthesizing the molecular sieve SSZ-13 using a reduced dose of TMAA+ as a structure-directing agent. The dose of TMAA+ cation may be significantly reduced by adding benzyl quaternary ammonium ions which worked together with TMAA+ cations as the structure-directing agent for reactants. Although such synthesis method effectively reduces the cost, the expensive TMAA+ cation is still used.
It is disclosed in the description of Patent No. 60/882,010 filed by Miller on Dec. 27, 2006 that a method for synthesizing the molecular sieve SSZ-13, wherein N,N,N-trimethyl-1-adamantyl alkyl amine cation is partially replaced with benzyl trimethyl quaternary ammonium ion (BzTMA+) as a structure-directing agent.
Although benzyl trimethyl quaternary ammonium ion has a relatively low price, it cannot become the most suitable structure-directing agent due to its irritation and harmful effect on humans.
In view of these reasons, the present invention is proposed.